Such a device is well known to a person skilled in the art, in particular for example from the patent document FR 2 907 695, which describes a machine, referred to as a drilling unit, having a drive mechanism provided with a drive pinion that is mounted in a fixed manner in terms of rotation on a tool holding spindle so as to rotate the latter while allowing said drive pinion to move axially, and a feed pinion coupled to the tool-holding spindle by a helicoidal connection so as to drive the spindle translationally along its axis, in a feed movement, depending on the relative rotational speed of the drive pinion and feed pinion.
Unlike numerical control machines or other drilling means that use electric motors, drilling units generally only have a (pneumatic or electric) motor which rotates the tool, via the drive mechanism, about its axis and simultaneously feeds it or returns it by translational movement along its axis. Since the translational and rotational movements are mechanically connected, the operational parameters of the drilling units are fixed by the choice of pinions and are constant throughout the drilling cycle. In particular the ratio between the rotational speed and the feed rate is imposed kinematically, thereby giving a constant feed per revolution, which therefore cannot be adapted optimally depending on the materials drilled. Thus, if such a machine proves to be generally satisfactory, it can prove tricky to use it to drill deep bores and/or multimaterial stacks.
Specifically, in this context, it can prove difficult to evacuate chips formed during drilling. If chips become jammed, this can result in the breakage of or significant wear to the drilling tool, deterioration of the state of the surfaces generated, more particularly during operations of drilling stacks made of different materials, or a significant drop in productivity, in particular by the limitations imposed by the cutting parameters such as the speed of rotation or the feed rate.
One remedy to this drawback consists in causing the breakup of these chips by varying the thickness thereof, by virtue of discontinuous drilling. Thus, the drilling machine described in the abovementioned patent document is provided with a system of displacing the feed pinion with respect to the casing of the machine, said system being in the form of a cam/cam follower assembly, a first of these elements being fixed in terms of rotation to the spindle and the other being fixed in terms of rotation to the feed pinion, making it possible to impose an oscillating movement on the feed movement of the spindle along its axis during drilling. Thus, during the feed of the drilling tool, these axial oscillations vary the thickness of the chips, thereby allowing them to be broken up and evacuated. However, this results in friction at the cam, which causes heat, wear and noise. Moreover, the frequency of the oscillations depends on the relative speed of rotation between the feed pinion and the tool-holding spindle and does not always make it possible to obtain optimal oscillation frequencies for good breakup of the chips, since the number of oscillations per revolution remains constant. Consequently, such a machine could not be adapted to multiple machining configurations, for example to drilling with drill bits having two edges or with a single edge, for which the number of oscillations per revolution needs to be different. Moreover, the architectures proposed by the abovementioned patent did not make it possible to be able to stop oscillation excitation depending on the nature of the machining process. However, such a stop may become necessary, for example if the same tool needs to carry out drilling followed by the production of a bevel, the latter requiring a feed movement without superimposed oscillations. Further optimizations of the vibrating assistance for the breakup of the chips are also impossible with known principles, for example real-time variation, during the drilling operation, of the amplitude or the frequency of the imposed oscillations, or the generation of oscillation shapes other than a sinusoid, for example a sawtoothed oscillation shape.